1. Field of the Invention
The present invention relates to electrophotographic toner compositions. More particularly, the present invention is concerned with processes for producing improved electrophotographic toner compositions.
2. Description of the Prior Art
In general, those developers used in electrophotography are subjected to vigorous mechanical friction during the course of development. Therefore, usual developer compositions contain those resins having high mechanical strength, for example, tough, high molecular weight resins.
These resins, however, have the disadvantage that, since a large quantity of heat is required in fixing them on a support, such as paper, when the intention is to increase the rate of development of an electrophotographic duplicator equipped with a heat roll-type fixing unit, a large scaled apparatus for generating a large quantity of heat or for removing the heat generated is needed.
In order to eliminate the above defects, those developers containing low molecular weight resins have been proposed. While these developers eliminate the above defects, they inevitably have the disadvantages that when a heated roll-type fixing unit is employed, a decomposition of the low molecular weight resins takes place at the time of fusing, they adhere not only to a support, such as paper, but also adhere to heated rolls, thereby forming a film on the heated rolls, and the phenomenon called "off-set" occurs when they are used.
Thus, to remove the above-described defects, electrophotographic toner compositions containing cross-linked resins have been developed. These compositions have many advantages. For example, they have high mechanical strength and good grindability, they can be fixed at relatively low temperatures and off-set scarcely occurs when they are used.
These electrophotographic toner compositions containing cross-linked resins are usually produced by a method comprising the following steps:
(1) a polymerization step in which the monomers are polymerized; PA1 (2) a cross-linking step in which a cross-linked resin is obtained by cross-linking; PA1 (3) a melt-kneading step in which the cross-linked resin, a colorant and the like are kneaded; and PA1 (4) a pulverizing step in which those particles having the desired size are obtained.